Effects of Admixtures on the Anti-oxidation Property of MgO/Si_3N_4 Composite Refractory

The effect of the admixtures of Al and Si metals and B4 C and MgAlON compounds on the oxidation of MgO/ Si3N4 composite refractory has been studied, which is a promising carbon free refractory for steel-making application . The four kinds of admixtures can be used as anti-oxi-dants for Si3N4, but the mixture of Al and Si achieved the best result. The mixture can not only play the role as anti-oxidant, but also assist the sintering process and help form dense sintering layer, improving the property of the composite.

Development and Characterization of Ceramic Matrix Composite (CMC) from Nigerian Kankara Kaolin and Gray Cast Iron Filling

This study developed a ceramic composite material (CMC) for use as a refractory material from “Kankara” clay (kaolin) as a matrix material mixed with gray cast iron (GCI) as reinforcement. The CMCs were prepared by varying the percentage by weight of the gray cast iron using 5, 10, 15, 20, 25, 30, 35, 40 and 45 wt%. Tests were conducted on the developed CMC, using standard test techniques, to determine physical and the mechanical properties of the produced composites. The results for mechanical properties showed improvement in the hardness value from 47% at 5% GCI content to 94% at 45% GCI content;the compressive strength improved from 3.11% at 5% GCI to a peak of 7.15% at 25% GCI and then descended down to 3.74% at 45% GCI content while the ultimate tensile strength improved from 0.75% at 5% GCI to a peak of 1.87% at 25% GCI down to 1.34% at 45% GCI content. Equally, there is an increase in bulk density from 1.74% for 5% GCI content to 2.09% for 45% GCI contentment. The linear shrinkage reduced from 11.57% to 1.15%;water absorption also reduced from 33.68% to 15.20%;apparent porosity too reduced from 42.2% to 16.02%. However, cold crushing strength initially increased with increase in GCI content from 3.89 to a peak of 13.32 V for 25% GCI content and progressively dropped to a value of 5.25 V at 45% GCI content. All the values obtained from the blends are within the recommended values for kiln shelves. However, the CMC developed on 25% GCI content showed the best combination of both mechanical and physical properties required of a good material for the production of kiln shelves.

Preparation of Composites by Nitro Aluminothermic Processes, over β–SiAlON Matrix in the SiAlON-SiC-Al2O3 System

Goal: The goal of the research is preparation of SiAlON-containing composite through nitro aluminothermic processes, by the methods of reactive sintering and hot compaction. Method: The composite CH-6 was obtained by the method of reactive sintering, with further grinding and hot compression in vacuum furnace at 16000°C, under 30 MPa pressure and 10-12 min standing at the final temperature. Precursor was prepared in a thermostat at 150°C temperature by double compression. Pressure equaled to 20-25 MPa. Results: Physical-technical properties of specimens prepared via hot compaction were investigated. Mechanical strength at compression is 1940 MPa;mechanical strength at bending is 490 MPa;elastic module is 199.5 GPa, HV-11.6 GPa. X-Ray diffraction analysis, electron microscopic and X-ray diffraction Microspectral analysis were used to investigate composite microstructure and phase composition. Composite formulation was defined, the main phases of which were: β-SiAlON, corundum and silicium carbide. Conclusion: Composite CH-6 has been selected from the obtained composites, which is characterized by relatively high physical-technical properties: strength, density and hardness. Materials can be used for making high refractory articles, such as jackets to secure thermocouples, furnace bedding, cutting tools for metal and wood treatment, in rocket spatial technology and others.

Outstanding specific yield strength of a refractory high-entropy composite at an ultrahigh temperature of 2273 K

We reported on the mechanical properties and microstructural evolution of a W_(20)Ta_(30)Mo_(20)C_(30)(at.%)re-fractory high-entropy composite(RHEC).The RHEC exhibited outstanding yield strength at both 2273 and 1873 K.Microstructural investigations revealed that the as-cast RHEC had a triple-phase structure con-sisting of FCC dendrites,HCP matrix,HCP-BCC eutectic structure,and FCC-BCC eutectoid structure,and exhibited high-density defects owing to the complex phase transformations during solidification.After annealing at 2273 K,the precipitation of the BCC phase from the FCC dendrites and the decomposition of the HCP phase into the FCC-BCC eutectoid structure was observed to significantly refine the grain sizes of all triple phases.After compression at 2273 K,the ceramic phases and solid solution precipitated out from each other,which helps to avoid persistent softening after the yielding of RHEC.Further analyses sug-gested that the dominant deformation mechanisms of the BCC phase and HCP phase are dislocation glide and transformation-induced plasticity;whereas those of the FCC phase are twinning-and transformation-induced plasticity.The outstanding yield strength of this RHEC at ultrahigh temperatures may originate from the high-content ceramic phases and the structural metastability of the multi-principal composition.These findings provide a novel strategy to design RHECs by alloying high-content nonmetallic elements,which contributes to further breaking through their performance limits at ultrahigh temperatures.

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti_(5)Si_(3) was prepared by adding Si into MoNbTaTiV high-entropy alloy.The obvious oriented in situ Ti_(5)Si_(3) phase formed eutectic phase with BCC phase in the inter-dendritic area,which leads to excellent properties of the composite.The alloy exhibits ultra-high yield stress of 718 MPa at 1200℃ and obvious compression plasticity.After reaching the maximum strength,dynamic recovery(DRV)and dynamic recrystallization(DRX)caused soften phenomena.The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction.The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms,while the Ti_(5)Si_(3) phase has a geometric DRX mechanism in addition to the above two mechanisms.The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.